The invention relates in general to the field of electronically commutated, brushless DC motors. These kinds of motors may find application in a variety of different areas such as in automobile technology for blowers, coolant pumps or to support the steering system. Other areas include, for example, fan blowers in power supplies or spindle motors in hard disk drives for data processing systems, to name but a few possible applications.
An electronically commutated, brushless DC motor basically consists of a shaft, a rotor assembly having one or more permanent magnets arranged on the shaft and a stator assembly comprising a stator core and phase windings. Two bearings spaced apart axially are arranged on the shaft for the purpose of journaling the rotor assembly and the stator assembly with respect to each other.
FIG. 1 shows a schematic diagram of a circuit to drive a three-phase DC motor. In the illustrated embodiment, the control circuit comprises six power transistors as well as other control electronics, not illustrated in the drawing, which control the operation of the DC motor. In the prior art it is standard practice to set up the control electronics for the DC motor on a printed circuit board as a closed unit which is plugged into the motor or connected to the motor in some other way. The electronic circuit board is connected to the motor via connecting wires and leads which are connected to the circuit board through soldering, using connectors or any similar means. Plug-in and soldered connections, as well as the length of the leads, increase the electrical resistance of the DC motor and consequently reduce the electric voltage available at the motor windings.
The power components of an electric motor, particularly a heavy-duty electric motor in a harsh environment, such as in a motor vehicle, are often heated to temperatures of over 100° C. To avoid overheating, it is therefore necessary to cool such power components in order to prevent their premature breakdown.
On the other hand, it is necessary to accommodate the power components as well as the control components of the electric motor on electrically insulating circuit boards and to connect them to each other. It is thus common practice to make the substrate of conventional circuit boards from a plastic having good electrically insulating properties. A plastic of this kind, however, has poor thermal conductivity.
A circuit board material which is not only electrically insulating but also conducts heat well is known (company publication “The T-Lam System—T-Guide for performance”, THERMAGON Inc., Ohio/USA, 16, Nov. 1999).
The object of the invention is to provide an arrangement to accommodate the power and control electronics of an electric motor which meets the requirements, on the one hand, for good thermal conductivity of the heat generated in the power components and, on the other hand, for good electrical insulation of both the power components and the control components, combined with a simple, space-saving, low-cost design and construction.